A jeweler has a 20 gram ring that is 60% gold and 40% silver. He wants to melt it down and add enough gold to make it 80% gold. How many grams of gold should be added?
(a) 4 grams (b) 8 grams (c) 12 grams (d) 16 grams (e) 20 grams
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,.上期答案:(b) 420.